Gold is a precious metal, used as a colorant (pigment) in powdered form, with color index CI 77480. It is brown, chemically relatively inert, and stable to oxidation and other changes.
The EC strictly regulates the use of gold in decorative cosmetics. Purity is regulated by Directive 95/45/EC (E175) and (EC) 2009/1223, and it is included in the allowed colorants annex: listing 133 in Annex IV. It was also used as a food additive under the designation E175 and is considered non-toxic, but its use in food is restricted in some countries.
Scientific studies show that the key factor in gold's safety in cosmetics and jewelry is its purity. Adverse effects and allergic reactions are mainly related to contamination with other metals in gold alloys, or to their ionic forms in salts or organic complexes.
The skin absorption rates of elemental gold are very low due to its low solubility. However, in ionic (Au+ and Au3+) or nanoparticle form (especially in colloid systems), it can pass through the skin barrier. CI 77480 is considered a safe ingredient for external use in cosmetics. Some cases of hypersensitivity reactions have been reported, with subclinical signs including lichen planus and skin eruptions.
